Radioreceiving system



H. H. BEVERAGE.

RADIORECEIVING SYSTEM.

APPLICATION FILED MAY 25, |92l-.

1,4}3%,986. Patented. Nov. 7, 1922.

Fgl.

Inventor:

Harold H. Sewerage.

by/ww His Attorney.

EARQLD GE, 0Z5 EIVEEl-IEAD, I

BADIOEZEGEEV Application filed Slay 25, 1.923..

2"0 all whom it may cancer lie it known that l, Harrow) H. BEVERAGE. a citizen of the lnited States. residing at ltiverhead, in the county of Suffolk, State of New York, have invented certain new and useful improvements in lladioreceiving Sys tems. of which the following is a speciiication.

My present invention relates to radio receiriup systems, and more particularly to means for preventing interference in such systeu'is by waves of a wave length in the neighborhood of that of the waves which are to he received and which are traveling in the same direction as the waves to be received.

in my copending application, Serial No. 372,933, filedApril 10, 1920, issued on June 7, 1921, asPat ent No. 1,381,089, 1 have de scribed an improved form of unidirectional antenna by means of which signals coming from a given direction may be readily received and applied to the receiving apparatus to the exclusion of signals coming from the opposite direction. lln some cases, however, it will be desirable to be able to receive signals coming from the desired direction when there are also present in' the antenna strong currents produced by signaling waves coming from the same dinection as that of the desired signals and produced by waves of a wave length near that of the desired signal waves and produced by transmitting stations much nearer to the receiving station than the transmitting station from which it is desired to receive signals.

The object of my present invention is to provide means for permittin of the desired reception in a case such as t at referred to where the ordinary tuning customarily employed in the receiving circuit will not offer a high enough degree'of selectivity to effcctively eliminate the interference of signaling waves. The unidirectional antenna which l have described in my application referred toabove is preferably untuned so that it odors no discriminating selectivity between the desired signaling waves and interfering waves. In order to provide the desired selectivity and prevent the interfering waves from being impressed upon the receiving apparatus it provide in conjunction with the circuits whereby the desired signaling currents are impressed upon the receiving apparatus, one or more resonant cir= rive cuits tuned to the frequency of the fering waves and arranged in such a way as to form what l term interference shunts for absorbing currents produced by the interfering waves, and thus preventing these currents from being impressed upon the receiving apparatus.

The novel features which i believe to be characteristic of my invention are set forth in the appended claims. My invention itself, however, both as to its organization and method of operation will be best under-, stood by reference to the following description taken in connection with the accompanying drawings in which Pi s. 1, 2 and respectively show three different circuit an rangements, whereby my invention may carried into effect; Fig. i is a diagrammatic representation of a circuit which is the equivalent of the circuit of Fig. 3 and Fig. 5 is a representation of tuning curves which may be obtained in the receiving system under different conditions of operation.

As indicated in the drawings, I employ a long horizontal antenna which is preferably c made up of two parallel conductors 1 and it which are grounded at the ends 3 and 4-. turrents received upon this antenna by signaling waves traveling through the other from the end toward the end 3 will be substantially zero. value at the end 4-, and will increase to a maximum value at end 3. 0n the other hand, currents produced in the antenna by other waves traveling from the end. 3 to the end i will be of substantially zero value at the end 3 and will be of a maximum value at the end at. i therefore, it is desired to receive signaling waves travcling from the end 4- toward the .end 3, the signaling currents produced in theantenna at the end 3 may be impressed upon the receiving apparatus without any interference from currents produced by waves traveling in the opposite direction.

It may not, however, be convenientto lo- I cate the receiving apparatus at the end 3 or the antenna, in fact, for reasons which it is unnecessary to set forth in detail, it may be desirable to locate the receiving apparatus at the opposite end. in order to permit of such location of the receiving apparatus the ground connection at the end 3 may he made through the primary 5 of the transformer, the secondary 6 of which has its terminals connected respectively withconductors l and 3 2. The conductors 1 and 2will then serve as a transmission line for transmitting the desired signaling currents from the end 3 to the opposite end. The conductors 1 and 2 thus form the two sides of a transmission line in which the desired si aling currents will flow in opposite directions.

The middle point of transformer secondary 6 is connected to ground at 3, andat the opposite end of the antenna the middle point of the primary winding 7 by means ofwhich the desired signaling currents will be impressed upon the receivln apparatus, is also connected to ground. y 'reason ofthis connection currents produced in the antenna by waves traveling from the end 3 toward the end 4 and which flow in the same direction through conductors 1 and 2, will be divided equally between the two halves of the primary 7 and will produce no effect in the secondary 8." If the ground connection at 4 is made through a resistance 9 having a value substantially equal to the surge impedance of the antenna, there will be no reflection of the signaling currents flowing toground at 4. These currents will then produce no interference with the reception of the desired signaling currents transmitted over the conductors 1 and 2 of the transmission line.

This arrangement, however. will not offer any selectivity between currents produced in the antenna by waves traveling in the same direction as the desired signaling waves. llf it happens that there is a transmitting station located much nearer the receiving station than the transmitting station from which the desired signals are to be received and this near-by transmitting station is operating at a wave len th in the neighborhood of that of the esired signaling waves, it will be diflicult to eliminate the interference from the near-bystation by means of the usual tuning circuits employed with the ordinary receiving apparatus. The actual receiving apparatus employed, which I haveindicated merely by the rectangle 10 may be of any desired type. In order to avoid such interference I provide a resonant circuit made up of inductance 11 and capacity 12 which is connccted in shunt to the primary 7 and which is tuned to the frequency of the interfering waves. The impedance of this shunt circuit to the interfering currents will be so low in comparison with the impedance of the primary 7 that the effect of these interfering currents in the secondary 8 will be substantially eliminated.

The nature of the results which are obtained by the arrangement which i have described is indicated by the tuning curve shown in Fig. 5. which illustrates results which have been obtained under actual operating conditions. The tuning curve A rep left-hand side of the tunin resents an actual tuning curve obtained in the receiving apparatus upon si als of a wave length of 14,200 meters without any interference shunt and with a near-by station operating at a wave length of 13.900 meters. \Vhen an interference shunt tuned to the 13,900 meter wave length was employed the curve was shifted to the full line curve ,By using a second interference shunt 13 tuned to a wave len th of 14,500 meters the right-hand side of the tuning curve is shifted to the dotted'line C. Thus it will be seen that by the use of an interference shunt in the-manner described it is possible to eliminate all effect in the receiving apparatus of interfering waves differing in frequency from the desired signaling waves by only 300 meters without producing any appreciable weakening of the desired signaling currents.

An interference shunt such as I have described may in some cases be more effectively employed in abridge circuit such,

for example, as that shown in Fig. 2 of.

the drawing. In this case the two halves of the winding 7 form two arms of the bridge, the interference 'shunt made of inductance 14 and capacity 15 forms the third arm, and variable resistance 16 forms the fourth arm. This bridge circuit may balanced by tuning the shunt to the interfering wave and then ad'usting the resistance 16 until the inter ering signal disappears. The points 17 and 18 to which the receiving apparatus 10 "is connected will then be at equipotential points with respect to the interfering wave and the interference will be eliminated. The bridge, however, will not be balanced for the desired signals and the points 17 and 18 will not beat the same potential with respect to the desired signalin waves.

in Fig. 3 I ave indicated another bridge arrangement in which two interference shunts are employed which are tuned for interfering frequencies above and below that of the desired signals. In this case the arms 19 and 20 of the bridge are each made up of two parallel interference shunts 21 and 22, while the other two arms of the bridge are formed by resistances 23 and 24. When the interference shunts are tuned to the two frequencies, one above and one below the desired signals, the points 25 and 26 to which the receiving apparatus is connected will be equipotential points with respect to si nalin waves of the two frequencies for w ich tie interference shunts are tuned. The bridge, however, will not be balanced for the desired signals and these signals will consequently be impressed upon the receiving apparatus without interference from the interfering waves.

lt we assume that the interference shunts 21 are tuned to a frequency slightly above best I the shunts 21 will tune to frequency. in Fig. 4 I have that of the desired signals, then the resultant impedance of the shunts 21 for the desired. signals will be inductive and if the shunts 22 are tuned to a frequency slightly below that of the desired signals the resultin impedance of the shunts 22 for the desire signals will be capacitive. Ifthe constants are properly chosen the inductive reactance of the capacitive re for the signaling indicated the equivalent circuit which would then be formed for the desired signaling frequency. In this circuit, it will be seen, the two arms 19 and 20 of the bridge form two substanactance of the shunts 22.

tially infinite impedance traps for the signaling frequency. The result therefore is the same as though the desiredsignahng currents were impressed upon the receiving apparatus through the resistances 23 and 24.

- It will be apparent that the same result may be obtained in the arrangement shown in Fig. 1 if the two interference shunts indicated are tuned-in the manner described, that is, these two shunts together form a frequency trap of substantially infinite impedance for the signaling frequency and the use of the interference shunts will in no way weaken the strength of the desired signaling currents.

While 1 have shown and described the preferred embodiments of my invention, it will be apparent that my invention is by no means limited to the exact circuit arrangements shown, but that many modifications therein may be made without departing from the scope of my invention as setforth in the appended claims. For example, while I have indicated the receiving apparatus as being located at the end of the antenna nearest the transmitting station from which signals are to be received. my invention may equally well be employed when the receiving apparatus is located either at the other end of the antenna or at some intermediate point.

\Vhat I claim as new and desire to secure by Letters Patent of the United States. is

1. The combination in a radio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus. means for impressing .upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction. and means for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon saidv receiving apparatus.

'2. The combinationin a radio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus, impressing upon'said receiving apparatus desired signaling currents produced in said direction as the circuit for impressing upon said means for antenna by waves traveling in a given direction and a resonant circuit which is tuned to' a diflerent frequency from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

3. The combination. in a radio receiving system of an aperiodic horizontal receiving antenna, areceiidng apparatus, a bridge circuit forimpressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, and means for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

4. The combination in a radio receiving system of an aperiodic horizontal receiving antenna. a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, one of the arms of said bridge comprising a resonant circuit which is tuned to a different frequency from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near "that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

5. The combination in a radio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, one of the arms of said bridge including two parallel resonant circuits which are tuned to two difierent frequencies from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same desired waves from being impressed upon said receiving apparatus.

6. The combination in a radio system of an aperiodic horizontal receiving antenna. a receiving apparatus, and a bridge receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction. one of the arms of said bridge including two parallel resonant circuits which are tuned 'to two different frequencies from that of the desired waves for preventing currents produced in said an-' tenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being receiving i impressed upon said receiving apparatus. the arm of said bridge which includes two parallel resonant circuits being so proportioned as to offer a substantially infinite impedance to currents of the desired signaling frequency.

7. The combination in a radio receiving system, of an aperiodic horizontal receiving antenna, a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents pro duced in said antenna by waves traveling in a given direction, each of two of the arms of said bridge including two parallel circuits which are tuned to two different frequencies from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

8. The combination in aradio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, each of two. of the arms of said bridge including two parallelcircuits which are tuned to two different frequencies from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus, each of the arms of said bridge which include two parallel resonant circuits beingso proportioned as to otter a substantially infinite impedance to currents of the desired signaling frequency.

9. The. combination in a' radio receiving system of an aperiodic horizontal receiving antenna. a receiving apparatus. means for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction. and means for preventing currents produced in .said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

it). The combination in a radio receiving system of an aperiodic horizontal receiving antenna. a receiving appaartus. means for impressing '-npon ..said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction anda pair of resonant circuits which are tuned to two frequencies. one above and one below that of the desired waves for preventing currents produced in said antenna bv waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

11. The combination in a radio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus, a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, and means for'preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

12. The combination in a radio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus, a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, one of the arms of said bridge comrpising two parallel resonant circuits which are tuned to two different frequencies, one above and one below that of the desired waves for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

13. The combination in a radio receiving system of an aperiodic horizontal receiving antenna. a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents pro duced in said antenna by waves traveling'in a given direction, one of the arms of said bridge comprising two parallel resonant circuits which are tuned to two different frequencies. one above and one below that of the desired waves for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus. the arm of said bridge which includes two parallel resonant circuits being so .proportioned as to offer a-substantially infinite impedance to currents of the desired signaling frequency.

14. The combination in a radio receiving system of an aperiodic horizontal receiving antenna. a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction. each of two of'the arms of said bridge including two parallel circuits which are tuned to two diflerent fre uencies. one above and one below that o the desired waves for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction es es as the desired waves from being impressed upon said receiving apparatus.

15. The combination in a radio receiving system of an aperiodic horizontal receiving antenna, a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus desired signaling currents produced in said antenna by waves traveling in a given direction, each of two of the arms of said bridge including two parallel circuits which are tuned to two different frequencies, one above and one below that of the desired waves for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus, each of the two arms of said bridge which includes two parallel resonant circuits being so proportioned as to ofier a substantially infinite impedance to currents of the desired signaling frequency. 4

16. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both endsand which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus, means for impressing upon said receiving apparatus currents flowingin opposite directions in the two wires of said antenna, and means for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as thedesired waves from being impressed upon said receiving apparatus.

17. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired di-' rection to flow in opposite directions through the two wires thereof, a receiving apparatus,

means for impressing upon said receiving apparatus currents flowing 1n opposite d1- rections in the two wires of said antenna,

and a resonant circuit which is tuned to a difierent frequency from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the'desired waves and travelin in the same direction as the desired waves rom being impressed upon said receiving apparatus.

18. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currentsproduced in said antenna by waves coming from a desired di that of the desired waves for quency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receivin apparatus.

19. he combination in. a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus and a bridge circuit for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, one of the arms of said bridge comprising a resonant circuit which is tuned to a different frequency from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

20. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus and a bridge circuit for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, one of the arms of said bridge including two parallel resonant circuits which are tuned to two difierent frequencies from preventing currents produced in said antenna bv waves of a frequency near that of the desired waves. and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

21. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal. wires means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus, and a bridge circuit for impressin upon said receiving apparatus currents iiiiwin in opposite directions in the two wires 0 said antenna, one of the arms of said bridge including two parallel resonant circuits which are tuned to two difierent frequencies ill Tilt) .sired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus, the arm of said bridge which includes two parallel resonant'circuits being so proportioned as to offer a substantially infinite impedance to currents of the desired signaling frequency.

22. The combination in a radio receiving system of an aperiodic receiving'antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus, and a bridge circuit for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, each of two of the arms of said bridge including two parallel resonant circuits which are tuned to two different fre quencies from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

23. The combination in a'r'a'dio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus. and a bridge circuit for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, each of two of the arms of said bridge including two parallel resonant circuits which are tuned to two different frequencies from that of the desired waves for preventing currents produced in said antenna by waves of a frequency near that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus, each of the arms of said bridge which include two parallel resonant circuits being so proportioned as to offer a substantially infinite im edance to currents of the desired signaling requency.

24. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair 0t parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof. a receiving apparatus, means tor impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, and means for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction comprises a pair of parallel horizontal wires,

Ineansfor causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus. means for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, and a pair of resonant circuits which are tuned to two frequencies. one above and one below that of the desired wave for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon the receiving apparatus.

26. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires. means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus. a bridge circuit connected to the two wires of said antenna for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, and means for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

27. The combination in a radio receiving system of an aperiodic receiving antenna. which is grounded at both ends and which comprises a pair of parallel horizontal wires. means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus, and a bridge circuitconnected to the two wires of said antenna for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, one of 'the'arms of said bridge comprising two parallel resonant circuits which "arev tunedntoutwo different frequencies, one abo've and onell'ie low that of the desired waves for preventing currents produced in said antenna by waves at frequencies above and below that of the produced in nee apes desired waves and traveling in the same di-' rection as the desired waves from being impressed upon said receiving apparatus.

28. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and-whichcomprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through the two wires thereof, a receiving apparatus, and a bridge circuit connected to the two wires of said antenna for impressing upon said receiving apparatus currents flowing in opposite directions in the two wires of said antenna, one of the arms of said bridge comprising two parallel resonant circuit s which are tuned to two diiierent frequencies, one above and one below that of the desired waves for preventing currents said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus, the arm of said bridge which includes the parallel resonant circuits bein so proportioned as to ofi-er a substantially infinite impedance to currents of the. desired signaling frequency.

29. The combination in a radio receiving system of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired'direction to flow in opposite directions through the two wires thereof, are oeiving apparatus, nected to the two Wires of said antenna for impressing upon said receivin apparatus currents flowing in opposite irections' in and a bridge circuit conthe two wires of said antenna, each of two of the arms of said bridge comprising two papallel to two different frequencies, one above and one below that of the desired waves for preventing currents produced in said antenna by waves of frequencies above and below that of'the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus.

30. The combination in a radio receiving system, of an aperiodic receiving antenna which is grounded at both ends and which comprises a pair of parallel horizontal wires, means for causing currents produced in said antenna by waves coming from a desired direction to flow in opposite directions through: the two Wires thereof, a receiving apparatus, and a bridge circuit connected to the two wires of said antenna for impressing upon said receivin apparatus currents flowing in opposite directions in the two wires of said antenna, each of two of the arms of said bridge comprising two. parallel resonant circuits which are tuned tovtwo different frequencies, one above and one below that of the desired waves for preventing currents produced in said antenna by waves of frequencies above and below that of the desired waves and traveling in the same direction as the desired waves from being impressed upon said receiving apparatus, each of the two arms of said bridge which include two parallel resonant circuits being so porportioned as to ofier a substantially infinite impedance to currents of the desired signaling frequenc In witness whereof, ll have hereunto set my hand this 23rd day of May, 1921,

HAROLD H. BEVERAGE.

resonant circuits which are tuned 

